arXiv subjects

Adam F. Falk

Publications and source records attributed to Adam F. Falk.

At least 37 records · Page 2Linked to original sources

arXiv1998

Hybrid Charmonium Production in B Decays

We study the production of charmonium hybrids in B decays. We use the operator product expansion and nonrelativistic QCD to organize the various contributions to this process. We express the decay rate in terms of a few matrix elements which eventually will be fixed by experimental measurements or calculated on the lattice. While the Fock state expansion is problematic for hybrids, in that there is no perturbative large mass limit, the operator product expansion still provides a model independent framework for phenomenological calculations of hybrid production and decay. We then use a simple flux tube model to estimate the branching ratio B -> psi_g + X, where psi_g is a J^{PC}=0^{+-} hybrid, the large production of which could help resolve the low charm multiplicity and semileptonic branching ratio observed in B decays. We also investigate the possible contributions of tensor charmonium production. We observe that it is unlikely for either effect to be large enough to play a significant role in resolving these problems.

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arXiv1997

Heavy Quark Effective Theory and Inclusive B Decays

I review the use of the Heavy Quark Effective Theory in the computation of total rates and differential kinematic distributions in inclusive semileptonic and radiative B decays. Particular attention is paid to strategies for the extraction of V_{cb} and V_{ub}.

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arXiv1997

Final State Interactions and New Physics in B -> pi K Decays

Within the Standard Model, and if one assumes that soft rescattering effects are negligible, the CP asymmetry A^dir_CP (B^\pm -> π^\pm K) is predicted to be very small and the ratio R = BR(B_d -> π^\mp K^\pm)/BR(B^\pm -> π^\pm K) provides a bound on the angle γof the unitarity triangle, sin^2 γ\leq R. We estimate the corrections from soft rescattering effects using an approach based on Regge phenomenology, and find effects of order 10% with large uncertainties. In particular, we conclude that A^dir_CP \sim 0.2 and sin^2 γ\sim 1.2 R could not be taken unambiguously to signal New Physics. Using SU(3) relations, we suggest experimental tests that could constrain the size of the soft rescattering effects thus reducing the related uncertainty. Finally, we study the effect of various models of New Physics on A^dir_CP and on R.

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arXiv1997

Hadronic Spectral Moments in Semileptonic B Decays With a Lepton Energy Cut

We compute the first two moments of the final hadronic invariant mass in inclusive semileptonic B decay, in the presence of a cut on the charged lepton energy. These moments may be measured directly by experiments at the Upsilon(4S) using the neutrino reconstruction technique, which requires such a cut. Measurement of these moments will place constraints on the nonperturbative parameters \barΛand λ_1, which are relevant for extracting the quark masses m_b and m_c, as well as the CKM angle V_cb. We include terms of order α_s^2β_0 and 1/m_b^3 in the operator product expansion, and use the latter to estimate the theoretical uncertainty in the extraction of \barΛand λ_1.

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arXiv1997

Phenomenology of New Baryons with Charm and Strangeness

The CLEO Collaboration recently has announced the discovery of an excited charmed and strange baryon. We estimate the expected width of this new member of the Xi_c family. We discuss the phenomenology of the excited csq and css states, and consider what additional charmed baryons might be observable in the future. We point out that the final state Xi_c + K could be an interesting new channel to examine.

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arXiv1997

The Theory of Heavy Baryons

I discuss the theory of heavy baryon spectroscopy, emphasizing predictions which follow from light and heavy quark symmetries.

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arXiv1997

V_{ub} from the Hadronic Invariant Mass Spectrum in Semileptonic B Decay

The hadronic invariant mass spectrum for the inclusive charmless semileptonic decay $B\to X_u e \barν_e$ is studied. Particular attention is paid to the region $s_H<m_D^2$, which may be useful for extracting the value of $|V_{ub}|$. The sensitivity of the spectrum to the parameter $\barΛ\equiv m_B - m_b$ is explored. Perturbative QCD corrections to $dΓ/ds_H$ of order $α_s^2β_0$ are calculated. For $s_H \sim \barΛm_b$ nonperturbative QCD effects are important and the shape of the invariant mass spectrum is controlled by the B meson matrix element of an infinite sum of local operators. The utility of the hadronic mass spectrum for extracting $|V_{ub}|$ is explored.

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arXiv1996

Quenched Chiral Perturbation Theory for Vector Mesons

We develop quenched chiral perturbation theory for vector mesons made of light quarks, in the limit where the vector meson masses are much larger than the pion mass. We use this theory to extract the leading nonanalytic dependence of the vector meson masses on the masses of the light quarks. By comparing with analogous quantities computed in ordinary chiral perturbation theory, we estimate the size of quenching effects, observing that in general they can be quite large. This estimate is relevant to lattice simulations, where the $ρ$ mass is often used to set the lattice spacing.

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arXiv1996

The Heavy Quark Expansion of QCD

These lectures contain an elementary introduction to heavy quark symmetry and the heavy quark expansion. Applications such as the expansion of heavy meson decay constants and the treatment of inclusive and exclusive semileptonic $B$ decays are included. Heavy hadron production via nonperturbative fragmentation processes is also discussed.

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arXiv1996

The Many Uses of Excited Heavy Hadrons

I discuss a variety of issues in the physics of excited bottom and charmed hadrons. Recent developments in spectroscopy, strong decays, and production in fragmentation and weak decays are reviewed.

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arXiv1996

New Predictions for Charmed and Bottom Baryons

I review the recent proposal that there are new isotriplet heavy baryons with masses approximately 2380 MeV and 5760 MeV. This prediction follows from the application of heavy spin-flavor and light $SU(3)$ symmetries to the observed charmed and bottom baryon states. It also entails assumptions about the spin and parity quantum numbers of the observed states which are different than is commonly supposed. The discovery of such states would imply that the nonrelativistic constituent quark model is a poor predictor of heavy baryon spectroscopy. I update the analysis in light of new data which have become available.

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arXiv1996

Resumming Phase Space Logarithms in Inclusive Semileptonic $B$ Decays

We study logarithms of the form $\ln(m_q/m_b)$ which arise in the inclusive semileptonic decay of a bottom quark to a quark of mass $m_q$. We use the renormalization group to resum the leading radiative corrections to these terms, of the form $m_q^2α_s^n\ln^n(m_q/m_b)$, $m_q^3α_s^{n+1}\ln^n(m_q/m_b)$ and $m_q^4α_s^n\ln^{n+1}(m_q/m_b)$. The first two resummations are trivial, while the latter involves a non-trivial mixing of four-fermi operators in the $1/m_b$ expansion. We illustrate this technique in a toy model in which the semileptonic decay is mediated by a vector interaction, before treating the more complicated case of left-handed decay.

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arXiv1996

A New Interpretation of the Observed Heavy Baryons

I suggest that the conventional assignment of quantum numbers to the observed charm and bottom baryons is not correct, as these assignments imply large violation of the heavy spin-flavor and light $SU(3)$ symmetries. I propose an alternative interpretation of the observed states, in which the symmetries are preserved. If these novel assignments are right, there is a new state with mass approximately 2380~MeV which decays to $Λ_c+γ$, and another with mass approximately 5760~MeV which decays to $Λ_b+γ$. Although such states have not been seen, neither are they excluded by current analyses.

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arXiv1996

Phenomenology of the $1/m_Q$ Expansion in Inclusive $B$ and $D$ Meson Decays

We apply a recent theoretical analysis of hadronic observables in inclusive semileptonic heavy hadron decays to the phenomenology of $B$ and $D$ mesons. Correlated bounds on the nonperturbative parameters $\barΛ$ and $λ_1$ are derived by considering data from $B$ decays and, independently, data from $D$ decays. The two sets of bounds are found to be consistent with each other. The data from $B$ decays are then are used to extract a lower limit on the CKM matrix element $|V_{cb}|$. We address the issue of the convergence of the perturbative expansions used in the analysis, and compare our bounds on $\barΛ$ and $λ_1$ to lattice and QCD sum rule results. Finally, we argue that a comparison of the analyses of $D$ and $D_s$ decays provides evidence for the applicability of parton-hadron duality in the semileptonic decay of charmed hadrons.

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arXiv1995

Hadron Spectra for Semileptonic Heavy Quark Decay

We calculate the leading perturbative and power corrections to the hadronic invariant mass and energy spectra in semileptonic heavy hadron decays. We apply our results to the $B$ system. Moments of the invariant mass spectrum, which vanish in the parton model, probe gluon bremsstrahlung and nonperturbative effects. Combining our results with recent data on $B$ meson branching ratios, we obtain a lower bound $\barΛ>410\,{\rm MeV}$ and an upper bound $m_b^{\rm pole}<4.89\,$GeV. The Brodsky-Lepage-Mackenzie scale setting procedure suggests that higher order perturbative corrections are small for bottom decay, and even tractable for charm decay.

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arXiv1995

Excited Heavy Mesons Beyond Leading Order in the Heavy Quark Expansion

We examine the decays of excited heavy mesons, including the leading power corrections to the heavy quark limit. We find a new and natural explanation for the large deviation of the width of the $D_1(2420)$ from the heavy quark symmetry prediction. Our formalism leads to detailed predictions for the properties of the excited bottom mesons, some of which recently have been observed. Finally, we present a detailed analysis of the effect of power corrections and finite meson widths on the angular distributions which may be measured in heavy meson decays.

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arXiv1995

Instantons and the endpoint of the lepton energy spectrum in charmless semileptonic $B$ decays

A recent calculation by Chay and Rey has shown that instantons may make a significant contribution to the lepton energy spectrum near its endpoint. Using an ansatz borrowed from the study of high energy baryon number violating processes, we investigate whether these corrections could spoil the relation between the nonperturbative contributions to this spectrum and to the photon energy spectrum in radiative $B$ decays. We find, in general, that this universality may well fail unless the spectrum is smeared over a region which is considerably larger than had previously been thought necessary. This result affects the possibility of performing a reliable measurement of $V_{ub}$ using inclusive decays.

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arXiv1995

Theory of Rare B Decays

Theoretical aspects of rare $B$ decays are reviewed. The focus is on the relation between short-distance interactions and physical observables. It is argued that there remain significant uncertainties in the theoretical treatment of certain important quantities. (Talk presented at the International Symposium on Vector Boson Interactions, University of California, Los Angeles, February 1-3, 1995)

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